I installed a 94 LT1/t56 into my 1987 Z28. I originally wired it up using the "LT1 wiring for dummies" write up. It cranked sputtered and died. I then purchased a painless harness thinking this was my problem, and it now does the same thing. I replaced the opti, three time (lifetime warranty) just to tripple check it, because the problem sounds like a timing issue, and no dice. If any of you have experienced anything like this please tell me how you fixed it.

 

I ran into the same problem with my LT1 swap. When I first got the engine I replaced the optispark and other electric components just so I would have a fresh starting point. However, when the opti got replaced it was installed wrong. The cam sprocket pin was not aligned with the index key on the opti, therefore causing it to be out of time.

To my knowledge there are a couple different styles of optisparks.
Vented and Non-vented.

I have the vented version (My engine is a 95'). If you have this version just make sure that cam pin is aligned with that the key(indent) on the opti.

Jay

 

Mine did that the second swap I did, and it turned out the FP relay wasn't letting the pump get full power to keep the fuel rail pressurized enough.

 

My FP seems to be functioning correctly, I'm getting about 42psi instantly upon turning the key. As far as the opti spline's, Im about 98% sure I indexed it correctly. Mine was said to be a 94 style motor, and I hope the guy that sold it to me was'nt wrong. Is there anyway I can check to see what type I have?

 

just going out on a long shot. vats?:P

 

I am assuming you are getting fire to the plug. If you are getting fuel and fire, the only thing left is wiring/PCM problems. Make sure your injectors are firing with a noid light. If they are not it is probably a VATS issue.

 

Even if you have VATS bypassed electrically(not programmed out), it would still start for a second or 2.

Test the coil, shbox.com has a pic/diagram showing how to test it. Spark plugs and plugwires good? Fuel injectors getting power? Checked for codes? If it had a programming error, it usually won't run either.

 

i have same problem! i have a 94 LT1 out of a TA, and had it rebuilt to a 383 to put in my 89rs. Had the computer re-flashed by fast chip and the wiring harness done by LT1 wiring, and i cant get the thing to start. i have spark and the injectors are pulsing, but i have no idea what to do next. if anyone has any idea, please help

 

The injectors may be pulsing at the wiring, but are you getting anything out of the actual injector itself? Someone, can't remember bought an engine and like 6 out of 8 injectors were plugged and no fuel was coming out of them.

 

when i had a simular problem i layed the fuel rail upside down and watched them pulse

 

guys all i have to say is thats why i chose a ls1, I have had too many problems with lt1 wiring. i hate to say it try unplugging your maf and putting it into limp mode. could possibly be your maf or ignition module, also check your grounds

 

im kinda new at this but i thought unplugging put the car into speed density mode not limp home. /shrug i dunno

 

well sort of, it puts the ecm into the low octane table and would be a good test to see if the maf is messed up, lt1 mafs are crap and go out all the time

 

Don't know if this is the same thing, but just in case...my LT1 has always been slow to start, and always sets code 42 (EST Grounded). I went through the diagnostic chart (I posted it a while back in text form), and it looks like it's caused on my car by a defective circuit in the PCM, which causes it to think that the ignition module isn't working and stop delivering fuel whenever battery voltage is low (i.e. during initial cranking). Apparently whenever a fault is present that sets a code 42, the PCM assumes no spark is getting to the engine and cuts fuel to avoid flooding. I don't know for sure that this is the cause, since I haven't swapped the PCM yet, but it seems like the only possibility (the wiring is good and I've replaced everything else in the ignition system!).

If you have a weak battery or a more severe version of this problem, that could account for what you're seeing. Mine will sometimes fire a little bit on initial cranking, when there's some unburned fuel in the manifold and cylinders, then sputter out, and finally start and run when battery voltage comes back up. You can check for it by either looking for voltage on the fuel injector connectors or using a noid light; if fuel is being delivered at first and then cutting out, it could be what I've described here. VATS is also a possible issue; I believe the computer delivers fuel for the first couple of seconds, and then if it hasn't seen the 50Hz square wave from the VATS module it cuts out.

You should definitely check codes on your PCM; on OBD1 systems like ours you can make it blink the code out on the check engine light by shorting positions A and B on the 12 pin under-dash ALDL connector, or positions 5 and 6 on the 16-pin OBD2 style connector. I've always read the codes using my ALDL cable and laptop with FreeScan. There are a lot of sources for these cables, since the circuit to adapt GM OBD1 signals to RS232 serial is very simple; I got mine from www.akmcables.com. If you have a laptop or a computer you can move near the car, I highly recommend this setup; if you also get TunerCat, you can reprogram the ECU pretty easily, and get rid of annoying stuff like VATS and skip shift. One note; since our PCMs have only one set of memory chips that contains the software for OBD1/programming communications as well as for running the engine, if the voltage on the PCM drops below 12 volts during the programming process, the chips will get garbage written to them, and the PCM won't work until the chips are removed and reprogrammed with an external flash burner. The guy at akmcables.com can do this, but it's a lot easier to avoid it in the first place by making a bench programming setup; he describes how to do that on his website.

 

thanks for all the info- i will let you guys know what happens. keep the info flowing from all the senior gearheads- you guys rock! i have learned more from this site than i ever learned on any subject in school. sorry to interject on your lt1 problem thread- i should make my own... lt1's are a headache

 

Same here, only seems like the injectors and the coil is not firing. Assumed it was a pcm connection so I went through all of those and those are sorted. Cranks awesome, have fuel pressure, no spark, doesnt feel like the injectors are firing (have yet to pull one out) and the ground wire off the coil will get hot as hell.

used "Wiring for dummies"
"need help with LT1 wiring"
A source from lt1swap.com
2 haynes manuals (really great help, highlight all the feeds and go"
numorous connector diagrams

There were a couple other threads that I printed out that may have helped along the way but i'm still not gatting this to fire, any ideas?


-mike